1. Field of the Invention
The present invention relates to a device for applying on a surface a liquid or semi-paste substance such as an ink or a paint containing volatile solvents.
The invention relates in particular to an industrial pen for writing on any surface and in which the ink refills are specially designed to receive fast-drying inks and therefore inks containing volatile solvents.
The device contemplated by the invention is mainly intended to mark various objects and especially metal parts, irrespective of the state of surface of such objects.
In other applications of the device which forms the subject of the invention, the ink can be replaced by any other liquid or pastelike product and said device is in that case a device for the application of said substance.
2. Description of the Prior Art
It is known that, in industry, certain marking operations have to be performed with an ink (usually opaque and viscous) which dries very rapidly.
This type of ink contains highly volatile solvents. It is therefore necessary up to the time of use to keep this ink in an absolutely air-tight envelope in order to prevent these solvents from evaporating. Otherwise the ink would lose its viscosity and would no longer be capable of serving the purpose for which it is intended.
There was described in French patent No. 1,041,438 a ball-point pen for writing, the pen body being so designed as to contain an ink refill tube provided at the end remote from the ball with a rubber plug which can be perforated by means of a hollow needle screwed on the end of the pen body. This hollow needle establishes an air communication between the exterior and the refill, thus permitting the flow of ink.
This arrangement is not applicable to substances for marking or the like since they are relatively viscous and contain highly volatile solvents In fact, the above-mentioned communication established by means of the hollow needle causes evaporation of the solvents and does not permit pressurization for ensuring discharge of the substance through the application head.
In the majority of instances, fast-drying inks are used in markers of the type consisting of a completely air-tight flexible metal tube mounted on a marking head which permits a flow of ink as soon as its tip is placed in contact with the surface to be marked.
This marking head, which is fixed on the end of the flexible metal tube containing the ink, is constituted by a hollow cone usually of steel and containing a ball-valve. This valve includes a helical spring having the function of maintaining a ball against the valve-seat constituted by the circular discharge orifice of said metal cone so as to shut-off said orifice Said ball, the diameter of which is scarcely larger than that of said orifice, extends partly beyond the tip of the writing head formed by said metal cone.
In consequence, when said writing head is applied perpendicularly to the surface to be marked, the ball penetrates into its housing while compressing the spring which had maintained it against its seat, whereupon the ink is permitted to flow between the circular lips of the discharge orifice of the marking head.
However, in order to permit the flow of ink contained in an envelope which is tight against ingress of air, it is necessary to exert a pressure of the fingers on the external walls of the flexible metal tube which constitutes the marker body in order to compensate for he partial vacuum produced by the escaping ink.
Markers of this type with flexible metal walls have long been known and operate satisfactorily for the application of fast-drying inks.
However, they are subject to certain disadvantages: they are delicate in an industrial environment and are liable to burst readily, thus resulting in a loss of ink and in stains which are made even more disagreeable by the fact that these types of ink are usually indelible and water-resistant.
These markers are also awkward to handle since a clamping action of the fingers on the walls of the flexible tube has to be combined with the movement of the hand which is writing
French patents No. 2,298,444 and 2,460,163 have provided a remedy for these drawbacks by making arrangements such that the flexible metal reservoir which contains the ink is enclosed within an air-tight casing supplied by a compressed air circuit, the object thereby achieved being to ensure that the pressure which is necessary for discharging ink to the marking head is exerted by the casing instead of the user's fingers on the flexible walls of said reservoir.
This supply of compressed air has the further advantage in accordance with French patent No. 2,460,163, by means of programmed pulses, of initiating at will the forward displacement of the marking head which is mounted on a piston with a restoring spring, with a view, for example, to placing said head in contact with a part to be marked which is presented on an assembly line. In this patent, however, consideration is given to a marking device which is intended to be employed in a stationary position since it has to be connected to a compressed air circuit.
In an alternative embodiment of French patent No. 2,298,444, provision is made for an autonomous manual marking device consisting of an ink refill with flexible walls enclosed within an air-tight cylindrical casing performing the function of a pen and supplied with compressed air by a hand-operated pump mounted on said casing at the end opposite to that of the marking head. The hand-pump makes it possible by means of a non-return valve to introduce into the air-tight cylindrical casing the compressed air which is intended to replace the pressure exerted by the user's fingers on the flexible walls of the tube containing the ink. However, in order to ensure good operation of a pen of this type, the pressure which has to be exerted on the flexible walls of the ink refill is relatively high (0.5 to 1 bar) and this calls for a relatively rugged and efficient manual pumping system. The pen in this case is a marking instrument which is excessively heavy to handle and inconvenient to use.
In order to discharge the ink to the marking head, a good solution therefore consists in producing action by means of a gas under pressure, not on the flexible walls of an ink refill, but directly on the ink itself. The necessary pressure is in that case extremely low in order to ensure good flow of the ink to the marking head and the pumping device can therefore be constituted by a very lightweight and economical assembly.
A device of this type for putting ink directly under pressure has been employed for the operation of certain industrial markers which have a rigid body containing a certain quantity of ink and which are intended to be discarded when empty. However, markers of this type are fairly expensive to manufacture with respect to the value of the ink which they contain.